From the Cloyster card:If you flip heads, you would only prevent normal damage during your opponent's next turn. That does not include damage from poison, burn, confusion, or anything else like that because those aren't considered damage; they are considered "placing damage counters," which is different.
"Flip a coin. If heads, prevent all damage done to Cloyster by attacks during your opponent's next turn"
Consider I roll heads. This "damage" includes also the special conditions included in some attacks?
Thanks in advance!
For example, if the opponent's attack said "Place 3 damage counters on the defending Pokemon," Cloyster's Withdraw attack would NOT prevent it.
Hope that helps!